Remarkable evolutionary changes in cell morphology during reactive polymer nanocomposite foaming are observed by controlled foaming of suspensions of montmorillonite clay in the oligomeric polyurethane component. Delaminated nanoplatelets, when present as a networked cluster in suspensions, are shown to have very high efficiency in generating gas embryos for bubble nucleation. In the post-nucleation foaming period, clay nanoplatelets show an additional de-wetting behavior. The packing fraction of clay platelets in suspension and the consequent suspension rheology affect the final foam morphology.